The present invention relates to method and apparatus for measuring the thickness of wet coatings or films.
It is often necessary to determine the thickness of a fluid or semi-fluid coating, i.e., so-called "wet film", on the surface of various objects such as inking rolls, paint mill rolls, I-beams, tubular ducts (inside and outside surfaces) and many other objects having flat, angled, or curvalinear surfaces.
Gauges have heretofore been proposed for measuring the thickness of wet films, as evidenced for example, by U.S. Pat. No. 2,167,652 issued to Hoch on Aug. 1, 1939; U.S. Pat. No. 2,507,592 issued to Euverard on May 16, 1950; U.S. Pat. No. 2,675,623 issued to Lewis et al on Apr. 20, 1954; U.S. Pat. No. 2,839,835 issued to Zollinger on June 24, 1958; U.S. Pat. No. 3,019,645 issued to Lake on Feb. 6, 1962; and British Pat. No. 685,238 issued to Scott on Dec. 31, 1952.
Such gauges are designed to roll along a film-containing surface in order to measure the thickness of the film. More particularly, a pair of surface-contacting rollers are mounted on a rotary axle. Between the rollers a thickness measuring structure is positioned which can be in the form of radially projecting pegs or an eccentrically mounted annular rib, for example, which are calibrated so as to present faces to be wetted. The pegs or ribs present faces which are located at different distances from the outer diameter of the rollers. By rolling the gauge across the surface, the faces situated above the level of the film will not be wetted, while those faces at or below such level will be wetted. The operator need only thereafter inspect the gauge and take the reading of that wetted face located the greatest distance from the periphery of the rollers.
Gauges have also been proposed which are in the form of thin polygonal plates (e.g., rectangular plates) having calibrated notches around the outer peripheral sides. By laying one edge of the plate on the surface to be measured, the measurement can be made by thereafter examining the gauge to identify the deepest notch whose inner end face has been wetted.
Although gauges of the aforementioned type can provide accurate measurement on flat surfaces, they may not be able to perform adequately on curved surfaces due to the span between the surface-engaging portions of the gauge. For example, if a gauge having axially spaced rollers is rolled along an internal or external surface of a curved duct in a direction parallel to the axis, the rollers will engage portions of the surface which are higher than the intermediate portion of the surface which is being measured. Hence, the calibrated measuring structure will be located too high to take an accurate reading. Similarly, if a polygonal plate-type gauge is laid upon such a surface such that the plane of the plate is disposed perpendicular to the axis of the curved surface, the end edges of one side of the plate will contact the surface at locations above that portion of the surface to be measured by notches on such side. Hence, accurate readings are not possible.
It is, therefore, an object of the present invention to eliminate or minimize problems of the above-captioned type.
It is another object of the invention to provide novel methods and apparatus for measuring the thickness of wet films.
It is yet another object of the invention to enable the thickness of wet films to be accurately measured on surfaces of virtually any shape.
It is still another object of the invention to provide a novel gauge which comprises a thin circular plate having calibrated notches around the outside periphery thereof.
It is a further object of the invention to provide a novel method of measuring the thickness of a wet film wherein an annular plate having calibrated notches around the outside periphery thereof is rolled along the surface being measured.